1. Field of the Invention
The invention is related to the field of fabrication of perpendicular magnetic recording media and, in particular, to the growth of certain multilayer structures of a recording media structure in a single sputtering process module of a multi-station manufacturing tool.
2. Statement of the Problem
Many computer systems use magnetic disk drives for mass storage of information. Magnetic disk drives have typically been longitudinal magnetic recording systems, where magnetic data is recorded as magnetic transitions formed with their magnetization aligned parallel to the disk surface. The surface of the disk is magnetized in a direction along a track of data and then switched to the opposite direction, both directions being parallel with the surface of the disk and parallel with the direction of the data track.
Unfortunately, data density requirements are fast approaching the physical limits. Overall data density (or areal density) may be improved by improving linear density and/or track density. To improve linear density, bit sizes on a track need to be reduced which in turn requires decreasing the grain size of the magnetic medium. As this grain size shrinks, the thermal stability of the written domains decreases. Therefore, materials with higher magnetic anisotropy are utilized thereby requiring higher magnetic fields to be reversed.
One way to achieve higher density recordings is with perpendicular recording. In perpendicular recording systems, bits of data are recorded with their magnetization perpendicular to the plane of the surface of the disk. A perpendicular magnetic recording disk is generally formed by depositing on a suitable substrate an adhesion layer, a soft magnetic underlayer (SUL) stack, a seed layer(s), an intermediate non-magnetic layer(s), a magnetic recording layer(s), a capping layer(s), and an overcoat structure. The adhesion layer is formed on the substrate to improve adhesion of subsequently deposited layers to the substrate. The soft magnetic underlayer (SUL) stack serves to concentrate a magnetic flux emitted from a main pole of a write element and to act as a flux return path back to a return pole of the write element during recording on the magnetic recording layer. The seed layer(s) provide a transition for the growth of crystalline thin films on the amorphous SUL layers. The intermediate layer(s) controls the crystallographic texture, grain size, and the segregation of the magnetic recording layer. The intermediate layer also serves to magnetically de-couple the SUL stack and the magnetic recording layer. The magnetic recording layer(s) act as a storage layer for the data encoded as bit transitions. The capping layer(s) are employed to improve the recording media writeability and noise performance.
The layers of perpendicular magnetic recording media are formed by sequentially sputtering the layers on the substrate. Each individual layer of the perpendicular magnetic recording media is sputtered in a separate sputtering processing module (station) of a multi-station thin film deposition tool. The following paragraphs describe a typical fabrication process for perpendicular magnetic recording media.
A substrate is loaded onto a carrier mechanism in a loading chamber of the fabrication tool. The carrier mechanism then transports the substrate to a first sputtering process module. The desired sputtering conditions are set for the first sputtering module, and an adhesion layer, such as AlTi, NiTa, etc, is sputtered onto the substrate. The carrier mechanism then transports the substrate to a second sputtering module.
The next three sputtering modules form an antiparallel (AP) SUL stack. To form the AP SUL stack, the desired sputtering conditions are set for the second sputtering module, and a first layer of the SUL stack, such as a CoTaZr-based alloy, is sputtered onto the adhesion layer. The carrier mechanism then transports the substrate to a third sputtering module. The desired sputtering conditions are set for the third sputtering module, and a second layer of the SUL stack, such as Ru, is sputtered onto the first SUL layer. The carrier mechanism then transports the substrate to a fourth sputtering module. The desired sputtering conditions are set for the fourth sputtering module, and a third layer of the SUL stack, such as a CoTaZr-based alloy, is sputtered onto the second SUL layer. The carrier mechanism then transports the substrate to a fifth sputtering module.
The next two sputtering modules form a multilayer seed layer. To form the multilayer seed layer, the desired sputtering conditions are set for the fifth sputtering module, and a first seed layer, such as a CrTi, is sputtered onto the third SUL layer. The carrier mechanism then transports the substrate to a sixth sputtering module. The desired sputtering conditions are set for the sixth sputtering module, and a second seed layer, such as NiW or NiWCr, is sputtered onto the first seed layer. The carrier mechanism then transports the substrate to a seventh sputtering module.
The next two sputtering modules form a multilayer intermediate layer. This intermediate layer is typically non-magnetic and serves to decouple the magnetic recording layer from the SUL. This layer also serves as a growth template for the magnetic layers that will be deposited in the next sputtering modules. To form the multilayer intermediate layer, the desired sputtering conditions are set for the seventh sputtering module, and a first intermediate layer, such as a Ru (low pressure), is sputtered onto the second seed layer. The carrier mechanism then transports the substrate to an eighth sputtering module. The desired sputtering conditions are set for the eighth sputtering module, and a second intermediate layer, such as Ru (high pressure), is sputtered onto the first intermediate layer. The carrier mechanism then transports the substrate to a ninth sputtering module.
The desired sputtering conditions are set for the ninth sputtering module, and a magnetic recording layer(s), such as a CoPtCr-based alloy, is sputtered onto the second intermediate layer. It has been found that improved recording properties can be derived if a plurality of magnetic layers (two or more) is employed as the storage medium. For example, the stack may include magnetic layers differing in composition and magnetic properties to generate a magnetically modulated recording structure across the thickness of the recording layer. This permits improvements in writeability, jitter, and signal-to-noise. Therefore, it is common in current-art media fabrication to employ a plurality of sputtering modules housing magnetic targets with different compositions to fabricate a compositionally modulated storage layer. The carrier mechanism then transports the substrate to a tenth sputtering module. The desired sputtering conditions are set for the tenth sputtering module, and a capping layer(s), such as CoPtCrB, is sputtered onto the magnetic recording layer. As in the case of the storage layer, it is also advantageous to employ a plurality of layers for achieving the functionality of the capping layer (improved writeability through exchange coupling of the recording layer with a softer overlayer, such as the cap layer, whose magnetization orientation is more easily altered by the writing field). At least two layers are employed in some designs with one of the layers mediating the exchange coupling between the storage layer and the cap. The carrier mechanism then transports the substrate to an eleventh sputtering module. The desired sputtering conditions are set for the eleventh sputtering module, and a first overcoat layer, such as IBD, is sputtered onto the capping layer. The carrier mechanism then transports the substrate to a twelfth sputtering module. The desired sputtering conditions are set for the twelfth sputtering module, and a second overcoat layer, such as CNx, is sputtered onto the first overcoat layer. The carrier mechanism then transports the substrate to an unloading chamber.
As is evident from the above fabrication process, twelve or more individual sputtering modules are used to form the perpendicular magnetic recording media. The number of different sputtering steps used for fabricating longitudinal recording media is usually less than twelve. Thus, many existing fabrication tools have less than twelve sputtering modules. Therefore, it was widely accepted in the industry that current-art fabrication tools developed for fabricating longitudinal magnetic recording media are inadequate for the manufacturing of perpendicular recording media. In order to fabricate the perpendicular magnetic recording media described above, disk drive manufacturers may have to update their fabrication tools, which comes at a very high investment. It would therefore be desirable to find ways to use existing fabrication tools to fabricate perpendicular magnetic recording media.